Referring now to FIG. 1, there is shown a cross-sectional view of a conventional (prior art) semiconductor laser 10. Semiconductor laser 10 comprises a substrate 12 of n-type conductivity GaAs having a pair of opposed surfaces 14 and 16. On the surface 14 is a current blocking layer 18 of p-type conductivity GaAs having a central opening 20 therethrough. The current blocking layer is about 1 micrometer in thickness and is doped with beryllium of a concentration of 1.times.10.sup.18 impurities/cm.sup.3. On the current blocking layer 18 and within the opening 20 is an n-type conductivity cladding layer 22 of Al.sub.0.7 Ga.sub.0.3 As. The cladding layer 22 is about 2 micrometers in thickness and is doped with silicon to a concentration of 1.times.10.sup.18 impurities/cm.sup.3. On the cladding layer 22 is an active layer 24 of n-type conductivity GaAs which is 0.1 micrometer in thickness and is doped with 5.times.10.sup.17 impurities/cm.sup.3 of beryllium. On the active layer 24 is a cladding layer 26 of p-type conductivity Al.sub.0.7 Ga.sub.0.3 As of a thickness of 2 micrometers and doped with 1.times.10.sup.18 impurities/cm.sup.3 of beryllium followed by a cap layer 28 of p-type conductivity GaAs of a thickness of 2 micrometers and doped with 5.times.10.sup.17 impurities/cm.sup.3 of beryllium. A negative electrode 30 of AuZn is on the surface 16 of the substrate 12 and a positive electrode 32 of AuGe/Ni is on the cap layer 28.
Referring now to FIGS. 2, 3 and 4, there are shown sectional views illustrating a known (prior art) method of making the semiconductor laser 10. As shown in FIG. 2, the current blocking layer 18 is first epitaxially depositing using molecular beam epitaxy (MBE) on the surface 14 of the substrate 12. Then, as is shown in FIG. 3, the opening 20 is formed in the current blocking layer 18 by etching away specific portions of the current blocking layer 18. As shown in FIG. 4, cladding layer 22, active layer 24, cladding layer 26 and cap layer 28 are then deposited in succession using molecular beam epitaxy. This is followed by the deposition and alloying of the negative electrode 30 and the positive electrode 32.
In the operation of the semiconductor laser 10, the application of a reverse bias to the current blocking layer 18 and the cladding layer 22 prevents current from flowing through the current blocking layer to the substrate 12. The current only flows through the portion of the cladding layer 22 which is in the opening 20. Thus, the opening 20 serves as a current channel with an oscillation region being limited to the current channel provided by the opening 20.
A drawback with this conventional semiconductor laser 10 results from the fact that wet or dry etching of the current blocking layer 18 is required to form the current channel. To carry out the etching step, it is necessary to remove the substrate 12 from a vacuum chamber in which the semiconductor layers are grown. This gives rise to contamination caused by oxidation of the current blocking layer interface or the adhesion of impurities to the resist used to masking the current blocking layer 18 for etching the opening 20. This degradation of the current blocking layer interface shortens the life of the device.